Air conditioning systems typically include a blower for circulating air to and from an indoor space to be heated or cooled and apparatus for cooling or heating the circulated air, depending on the mode of operation of the system (i.e., either heating or cooling mode). A device (e.g., a compressor) is also provided for circulating a heat transfer fluid (e.g., a vapor compression refrigerant) between indoor and outdoor heat exchanger coils, whereby the air supplied to the space is cooled or heated. When the system is a conventional air conditioning system (i.e., not a heat pump system), the indoor coil functions as a cooling coil (i.e., as an evaporator when a vapor compression refrigerant is used as a heat transfer fluid) to transfer heat from the air flowing across the outside of the coil to the heat transfer fluid flowing inside the coil, and the outdoor coil functions as a heating coil (i.e., as a condenser when a vapor compression refrigerant is used as a heat transfer fluid) to transfer heat from the heat transfer fluid flowing inside the outdoor coil to outdoor air flowing across the outside of the coil. When the air conditioning system is configured as a heat pump, the indoor coil functions as a cooling coil and the outdoor coil functions as a heating coil in the cooling mode, as in a conventional air conditioning system. However, in the heating mode, the functions are reversed (i.e., the indoor coil functions as a heating coil and the outdoor coil functions as a cooling coil).
When a heat exchanger coil is operated as a cooling coil (e.g., an evaporator), air flowing across the coil is dehumidified as well as cooled, causing condensation to form on the coil. This condensation must be disposed of to prevent freezing of the coil and damage to the surrounding building structure. Typically, a drain pan is located beneath the coil to receive condensate runoff. The pan includes an opening in a bottom part of the pan to conduct the condensate accumulated in the pan to an external drainage conduit. Drain pans of various types are known in the art, as exemplified by the following U.S. Pat. Nos. 4,474,232; 5,071,027; 5,511,386; 5,715,697; 5,966,959; and 6,360,911 B1.
It is advantageous to reduce water retention in the pan to the extent feasible, not only to reduce the likelihood of condensate spillage from the pan onto the adjacent building structure, but also to inhibit the formation of mold, rust and other undesirable byproducts of stagnant water in the pan. Further, air flowing through the heat exchanger coil may pick up moisture from excessive water accumulation in the pan, which may result in unwanted humidity in the air supplied to an indoor space.